What a great outlook. Love the boulder. I’d suggest native ground covers planted at the top and they’ll spill down. Good old pigface is hardy and a version of grevillea birthday candles would also be good. Have a look at the plant selector on Gardening with Angus site.

despite looking horrible until plants establish consider a collection of old tyres to step up the dirt bank, dump a load of big rough gravel and rocks over the tyres to help hold them down and create drainage and make informal steps and then dump a load of mulch over the gravel and add some pockets of native soil to plant a variety of native ground covers and of course, leave the fabulous rock face exposed and warn the kids about potential snakes and lizards sunning themselves on the rocks ..or when you win the lottery, invest in some giant boulders to match the rock face and let nature take over the planting

Vetiver Monto is your friend.

Not only is it fragrant and useful for basket weaving but it is also used for erosion control. Vetiver has incredibly deep roots that make it useful for this purpose. Monto is a cultivar that cannot set seed and escape into the wild, since vetiver is not native. You can get this plant from many wholesale nurseries in bulk as it's used for environmental remediation work.

The native version is lomandra, which again can be purchased in bulk from wholesalers that deal with environmental remediation work. I believe a lovely clumping grass like that will look beautiful and quite naturalistic in that setting. It will also make a feature of those boulders. You can then plant Grass tree's on the ridge which will be an amazing backdrop to your yard.

Lomandra

Vetiver

Plantings will undoubtedly be the cheapest option. Lomandra and vertiver are both fast growing.

Mattress gabions are another option. These are wire baskets filled with large rocks. Used most often on earth cuts on the side of highways. Most landscaping gabions are rectangular in shape. But mattress type are used roadside. This is a large flat, wire basket than spans over a cut filled with large rock. Once completed it looks quite good but it will not be cheap. The advantage is that it is instantaneous. These ones are quite fancy obviously used to make a water feature. But mattress gabions are good for creating an appealing and uniform look.

I immediately thought of a low Gabion wall.

Another option, it to lay down some erosion fabric and plant into this by making pockets https://www.allstakesupply.com.au/geotextile-filter-fabrics-erosion-control-matting/.